EP0044250A1 - Flat-screen display with two-dimensional elastic-wave scanning - Google Patents

Abstract

In this flat screen display system using two-dimensional OES scanning, the flat screen (1) consists of an underlying piezoelectric substrate (2) coated with a layer of piezoluminophore powder (3). On the substrate (2) are launched four elastic surface waves, whose directions are not collinear two by two. The first two pulsed waves are launched by two transducers (4 and 5) perpendicular to each other. The third constant amplitude is launched by a third transducer (6). The fourth wave is modulated by the information to be displayed and is launched by a fourth transducer (7). The pulsed waves are launched with respect to the modulated wave with a delay predetermined by the distance to be traveled by the modulated wave to reach the point corresponding to the modulation. Usable with camera described in patent 2,308,263 to constitute an interactive screen.

Description

The present invention relates to a flat screen display system using two-dimensional elastic surface wave scanning.

In French patent 2,308,263 filed by the present applicants, a two-dimensional scanning process of an image projected on a semiconductor film has been described by means of three elastic surface waves launched on the surface of an underlying piezoelectric substrate. , the directions of the three surface waves not being collinear two by two. The nonlinear interaction of the three waves, at the points where they are in phase, produces an elastic wave whose frequency is the sum of the frequencies of the three initial elastic waves and whose amplitude is a function of the light projected at these points on the semiconductor film. In producing a camera using this method, signal generators are used which supply the transducers with the signals necessary to generate the three initial elastic surface waves and an output circuit. tuned to the frequency of the interaction signal and connected to a pair of electrodes, one of which is above and the other of which is below the piezoelectric substrate.

In the technical article entitled "Nonlinear acoustoelectroluminescence" by AB Sherman, AA Dobrovolsky and VV Lemanov, published in the technical review "ELECTRONICS LETTERS" of January 3, 1980, Vol. 16, No. 1, pages 37 and 38, the interaction of an acoustic surface wave propagating on the surface of a piezoelectric medium on which is deposited a layer of powder of electroluminophoric material has been described. The variation in the intensity of luminescence as a function of the amplitude of the elastic surface waves exhibits significant non-linearity. As a result, luminescence can be modulated by frequencies which are frequency harmonics. elastic surface waves. In addition, as the brightness is a function of the modulus of the surface wave field, these frequencies must be even harmonics.

In the experiments described in the article mentioned above, a lithium niobate substrate was used as piezoelectric medium, and, as phosphor powders, gallium phosphide or silicon carbide.

An object of the present invention is to provide a two-dimensional screen display system which uses a surface elastic wave scanning method derived from that which has been described in French patent 2,308,263, already mentioned above, and an interaction between the elastic waves of the surface of the scan and a non-linear phosphor powder.

According to a characteristic of the invention, there is provided a display system on a flat screen in which the flat screen is constituted by an underlying piezoelectric substrate coated with a layer of piezoluminophore powder and on which four waves are launched. elastic surface, whose directions are not collinear two by two, the first two waves being pulsed, the third being of constant amplitude and the fourth modulated by the information to be displayed, the pulsed waves being launched relative to the modulated wave with a delay determined by the distance to be traveled by the modulated wave to reach the point corresponding to the modulation.

According to another characteristic, the module of the fourth wave is chosen so that the interaction signal of the four waves at the point to be displayed is in the most favorable part of the luminescence characteristic of the piezoluminophore powder.

According to another characteristic, the screen consists of three elementary screens with transparent substrates including piezolu powders minophores respectively emit fundamental colors.

According to another characteristic, the layer of piezoluminophore powder is divided into adjacent groups of three lines of powders whose compositions correspond respectively to the emission of three fundamental colors.

According to another characteristic, the display system is completed by a device in the form of a flat camera consisting of a piezoelectric substrate coated with electrodes, on which are launched three surface waves with pulses and directions corresponding to the first three waves of the screen, a pulse signal equal to the sum of the pulses of the four waves of the screen being applied to the electrodes, the wave resulting from the interaction of the three elastic waves and the signal being collected by an appropriate reception transducer whose the output signal is applied, after modulation by the information, to the transducer launching the fourth wave of the screen.

It should be noted that this device incidentally makes it possible to designate a point of the image to measure its coordinates and therefore obtain an interactive screen.

• la Fig. '1 est une vue schématique en perspective d'un système d'affichage sur écran plat, suivant l'invention,
• la Fig. 2 est un vue très schématique permettant d'illustrer comment les ondes acoustiques interagissent à la surface de l'écran de la Fig. 1,
• la Fig. 3 est un bloc-diagramme d'un système d'affichage comprenant L'écran de la Fig. 1,
• la Fig. 4 est une vue schématique d'un dispositif capable d'engendrer l'avance nécessaire au modulateur du système de la Fig. 3, et
• la Fig. 5 est une vue schématique d'un système d'affichage trichrome, suivant l'invention.
• Le système d'affichage de la Fig. 1 comprend un écran plat 1 qui est formé d'un substrat piézoélectrique 2, sur la surface duquel est déposée une poudre piézoluminophore 3. Sur la surface du substrat 2, autour de la couche de poudre 3, sont prévus quatre transducteurs 4 à 7, qui sont capables, d'une manière classique, d'émettre des ondes élastiques de surface dans les directions de leurs normales respectives, ou voisines de celle-ci si le matériau est anisotrope.

The characteristics of the invention mentioned above, as well as others, will appear more clearly on reading the following description of an exemplary embodiment, said description being made in relation to the accompanying drawings, among which:

• Fig. 1 is a schematic perspective view of a flat screen display system according to the invention,
• Fig. 2 is a very schematic view making it possible to illustrate how the acoustic waves interact on the surface of the screen in FIG. 1,
• Fig. 3 is a block diagram of a display system comprising the screen of FIG. 1,
• Fig. 4 is a schematic view of a device capable of generating the advance necessary for the modulator of the system of FIG. 3, and
• Fig. 5 is a schematic view of a three-color display system according to the invention.
• The display system of FIG. 1 comprises a flat screen 1 which is formed from a piezoelectric substrate 2, on the surface of which a piezoluminophore powder is deposited 3. On the surface of the substrate 2, around the powder layer 3, four transducers 4 to 7 are provided, which are capable, in a conventional manner, of emitting elastic surface waves in the directions of their respective normal, or close to it if the material is anisotropic.

The transducers 4 and 5 are, in general, perpendicular to each other, while the directions of the transducers 6 and 7 are arbitrary, provided that they are not collinear with the transducers 4 and 5, nor between them. The transducers 4 to 7 have dimensions such that the widths of the tracks, along which they launch elastic waves, cover the useful surface of the display screen. The input terminals of the transducers 4 to 7 are respectively connected to the outputs of signal generators 8 to 11.

More particularly, in the example described, the material of the substrate 2 is isotropic, such as a glass or better a piezoelectric ceramic or even a piezoelectric plastic, or anisotropic, such as a piezoelectric crystal, such as a quartz crystal, niobate of lithium, berlinite (AIP0 ₄ ), Bi ₁₂ GeO ₂₀ , or Bi ₁₂ SeO ₂₀ .

The piezoluminophore layer 3 can consist of gallium phosphide or silicon carbide, or other phosphors used in television.

If we refer to Fig. 2, which schematically represents only the surface of the substrate 2, the generator 8 delivers to the transducer 4 a signal in the form of pulses and of pulsation ω ₁ with a repetition period T, the generator 9 delivers to the transducer 5 a signal in the form of pulses and pulsation w ₂ with a slightly different repetition period T + ΔT, the generator 11 delivers to the transducer 7 a signal of constant amplitude and pulsation ω ₄ , while the generator 10 delivers to the transducer 6 a signal of amplitude modulated by information and pulsation ω ₃ . The widths of the pulses delivered by the generators 8 and 9 are equal.

Referring to FIG. 2, it is assumed that the pulses 12 and 13 were emitted at the same time. Therefore, at time t, in an elementary zone 14 which is approximately on the bisector of the angle of the transducers 4 and 5, there is an interaction between these pulses of pulsations ω ₁ and ω ₂ , as well as with the wave keep going no represented, emitted by 6 and the continuous pulse wave ω ₄ , not represented, emitted by 7. The interaction signal has a pulsation ω ₀ which verifies the following relationship:

définit la direction a ₄ et la pulsation ω₄ de l'onde à émettre par 7 par la relation suivante:

If we designate the directions of propagation of the waves emitted by transducers 4, 5 and 6 by at ₁ , at ₂ and at ₃ , where at ₁ and at ₂ are orthogonal, the vector k ₄ , which verifies the following relation:

defines the direction at ₄ and the pulsation ω ₄ of the wave to be emitted by 7 by the following relation:

tandis que les autres points ont une amplitude A₁ + A₃ + A₄, ou A₂ + A₃ + A₄, ou zéro. Dans la relation précédente, τ est le retard dû à la propagation de l'onde entre le transducteur 6 et le point 14. Si la réponse de la poudre piézoluminophore 3 est très non linéaire, la luminescence des points autres que le point balayé 14 sera négligeable. Par contre, la pulsation de l'onde w ₄ sera choisie pour que la luminescence du point balayé soit la plus favorable.Let A ₁ , A ₂ , A ₃ and A _{4 be} the amplitudes of the waves respectively emitted by transducers 4 to 7, where A and A ₂ are pulse amplitudes, A ₄ a constant amplitude and A ₃ a modulated amplitude, point 14, scanned at time t, will have an elastic amplitude A:

while the other points have an amplitude A ₁ + A ₃ + A ₄ , or A ₂ + A ₃ + A ₄ , or zero. In the previous relation, τ is the delay due to the propagation of the wave between the transducer 6 and the point 14. If the response of the piezoluminophore powder 3 is very non-linear, the luminescence of the points other than the scanned point 14 will be negligible. On the other hand, the pulsation of the w ₄ wave will be chosen so that the luminescence of the scanned point is the most favorable.

Of course, when the time t varies, the point 14 moves along the line L :. Furthermore, the offset between the successive pulses emitted by 4 and 5 respectively varies from one period to another so that the line L moves. The period of the pulses emitted by 4 is, for example, slightly longer, with positive AT, than those of the pulses emitted by 4 and the period following the synchronous emission described above, will see the emission of 5 slightly delayed by compared to that of 4. So, in this following period, the interaction zone 14 will describe a line parallel to _L but slightly shifted to the right. It therefore appears that the useful surface is swept by successive lines. The difference in period AT makes it possible to define the definition of the sweep.

As described above, the luminescence to be generated at the instant t at point 13 results from the amplitude A ₃ of the wave emitted by 6 at the instant (t - τ). Depending on the slowness of the wave launched by 6 and the position of the point to be scanned, it is therefore necessary to determine the advance which must be applied to the modulation. The determination of the advance can, of course, be carried out by means of delay calculation whose input receives the modulation with a fixed advance and whose calculation parameters are fixed by the slowness of the wave emitted by 6 and the relative scanning speed of point 14 with respect to the transducer 6. However, the determination of this advance can be obtained by simple analog means, as will be described in relation to FIG. 3.

In Fig. 3, there is shown the block diagram of a complete display system according to the invention. A device operating as a camera 15, of the type of the camera described in French patent 2 308 263 already cited, has its output connected to the carrier input of a modulator 16 whose second input is connected to the signal source 17 modulating. The output of the modulator 16 is connected to the transducer 6 of a screen 1.

Fig. 4 schematically represents the surface of the substrate 18 of the camera 15, on which four transducers 19 to 22 are provided. Above and below the substrate 18, electrodes are arranged, one of which is partially shown at 23. transducers 19, 20 and 22 occupy on the substrate 18 relative positions identical to those occupied by the transducers 4, 5 and 7 on the substrate 2 of the screen 1. There is shown in 6 ′, FIG. 4, the position corresponding to that occupied by the transducer 6 of 2. The transducer '21 is parallel to 6', but is arranged on the other side of the active area of the surface of 18 relative to 6 '.

The transducers 19, 20 and 22 are respectively connected to sources of respective pulse signals w ₁ , w ₂ and ω ₄ . The electrodes 23 are connected to the output terminals of a pulsation sourceω ₀ , as defined by equation (1).

The sources, not shown, supplying the transducers 19 and 20 operate in pulse mode and are synchronous with the sources 8 and 9. The sources, not shown, supplying the transducer 22 and the electrodes 23 operate continuously.

The scanning is produced by the two transducers 19 and 20 along a line L., corresponding to the line L in FIG. 2. Being given the emission of 22 and the application of the pulsation ω ₀ by 23, there is a phase agreement at the scanned point M which will re-emit towards the rear, that is to say towards the transducer 21 with a pulsation ω ₃ . The wave collected on 21 has a delay (θ-τ), where θ is the constant propagation time between position 6 'and the transducer 21.

The signal collected by 21 is modulated in 16 by the signal to be displayed on the screen and the signal thus modulated is applied to the transducer 6.

If we consider the point M scanned at time t, the signal collected by 21 at the same time corresponds to the signal of the point scanned at time (t + θ-τ). If the output signals of the pulsed sources 8 and 9 are delayed by θ, the corresponding point M of screen 1 is scanned at the instant (t + 6).

In other words, the transducer 6 launches a signal at the instant (t + θ - τ) for a point scanned at the instant (t + 0), that is to say exactly with the desired advance T.

The schematic perspective view of FIG. 5 shows how, by superimposing three screens 1, 1 ′ and 1 ″, according to the invention, whose substrates are transparent and whose respective piezoluminophoric layers emit in three fundamental colors, a color display screen is obtained. in this case, a single camera is sufficient to obtain the necessary advance on the transducers 6 of the three superimposed screens.

According to the invention, it is also possible to provide for depositing on the surface of the substrate of a screen a network of lines of piezoluminophores organized in groups of three corresponding to three fundamental colors. A modulation source 10 is then provided capable of delivering the modulation as a function of the color line scanned at this time. Of course, the network of lines is parallel to the scanning direction.

It should be noted that if the screen in FIG. 1 and the camera of FIG. 4, an interactive screen is obtained, that is to say a device making it possible to designate a point of the image to measure its coordinates. In this case, the modulation signal is directly due to the interaction of the object designating the point and the surface of the camera.

Claims (5)

1) Flat screen display system using a two-dimensional surface elastic wave scan characterized in that the flat screen (1) consists of an underlying piezoelectric substrate (2) coated with a layer of piezoluminophore powder ( 3) and on which four elastic surface waves are launched, the directions of which are not collinear two by two, the first two waves being pulsed, the third being of constant amplitude and the fourth modulated by the information to be displayed, the pulsed waves being launched with respect to the modulated wave with a delay determined by the distance to be traveled by the modulated wave to reach the point corresponding to the modulation. 2) System according to claim 1, characterized in that the module of the fourth wave is chosen so that the interaction signal of the four waves at the point to be displayed is in the most favorable part of the luminescence characteristic of the powder piezoluminophore. 3) System according to claim 1 or 2, characterized in that the screen consists of three elementary screens (1,1 ', 1 ") with transparent substrates whose piezoluminophores powders respectively emit fundamental colors. 4) System according to claim 1 or 2, characterized in that the layer 'of piezoluminophore powder is divided into adjacent groups of three lines of powders whose compositions correspond respectively to the emission of three fundamental colors. 5) System according to one of claims 1 to 4, characterized in that the display system is completed by a device in the form of a flat camera (15) consisting of a piezoelectric substrate coated with electrodes, on which are launched three surface waves with pulsations e, t directions corresponding to the first three waves of the screen, a pulse signal equal to the sum of the pulsations of the four waves of the screen being applied to the electrodes, the wave resulting from the interaction of the three elastic waves and of the signal being collected by an appropriate reception transducer whose output signal is applied, after modulation by the information, to the transducer launching the fourth wave of the screen.

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